1. Field of the Invention
The present invention relates to an apparatus for generating inductively coupled plasma (ICP), and more particularly, to an ICP generating apparatus incorporating a double-layered coil antenna to improve uniformity of plasma density around a substrate within a reaction chamber.
2. Description of the Related Art
Low voltage and low temperature plasma technology is used in the manufacture of semiconductor devices and flat display panels. Plasma is used for etching or depositing certain materials on the surfaces of wafers for fabricating semiconductor devices, or substrates for fabricating liquid crystal display (LCD) panels. Particularly, in etching or thin film deposition processes for manufacturing highly integrated semiconductor devices, the use of plasma equipment is increasing. Therefore, development of plasma generating apparatuses appropriate for etching, deposition, or other processes is important for the development of semiconductor manufacturing processes and equipment. The most important factors in the development of plasma equipment for semiconductor manufacturing processes are the capability to operate on large substrates in order to enhance production yield, and capability to perform processes for fabricating highly integrated devices. Specifically, in accordance with a recent increase in wafer size from 200 mm to 300 mm, enhancing uniformity of wafer treatment processes as well as keeping high plasma density have become very important.
Various types of plasma equipment have been used in conventional semiconductor manufacturing processes, e.g., a capacitive coupled plasma (CCP) type, an electron cyclotron resonance (ECR) type, a helicon type, an inductively coupled plasma (ICP) type, and a hybrid type combining two or more of the foregoing types. Among the various types of plasma equipment, the ICP type equipment is considered to be the best equipment for the 300 mm large-size wafers because the ICP equipment can generate plasma with high density and high uniformity and has a simple structure compared to the other types of plasma equipment. However, development of ICP equipment for 300 mm wafers is not easily achieved by simply changing the dimensions of existing ICP equipment for 200 mm wafers. There are plenty of limitations due to difficulties in designing antennas that are essential to ICP discharges.
FIG. 1 shows the structure of a conventional ICP generating apparatus. As shown in FIG. 1, the ICP generating apparatus includes a reaction chamber 10 including a space for generating plasma. An electrostatic chuck 12 for supporting a substrate, e.g., a wafer, is provided at a lower portion Within the reaction chamber 10, and a dielectric window 16 is formed in an upper cover 11 of the reaction chamber 10. A gas supply port 14 for supplying reaction gas into the reaction chamber 10 is formed at a sidewall of the reaction chamber 10, and a plurality of gas distribution ports 15 connected to the gas supply port 14 are provided within the reaction chamber 10. A vacuum suction port 18 is formed at the bottom of the reaction chamber 10 and connected to a vacuum pump 19 for evacuating the inside of the reaction chamber 10. Further, a coil antenna 20 for generating plasma within the reaction chamber 10 is provided above the dielectric window 16.
The coil antenna 20 is connected with a power source (not shown) for supplying radio frequency (RF) current. As the RF current flows in the coil antenna 20, a magnetic field is produced around the coil antenna 20, and in accordance with variation of the magnetic field as a function of time, an electric field is induced within the reaction chamber 10. At the same time, the reaction gas is supplied into the reaction chamber 10 through the gas distribution ports 15, and is ionized by collisions with electrons accelerated by the induced electric field to generate plasma within the reaction chamber 10. The generated plasma chemically reacts with the surface of the wafer W so that the wafer W is subject to a desired process, e.g., etching. Meanwhile, an additional RF power source (not shown) is generally connected to the electrostatic chuck 12 for supplying a bias voltage to increase the energy of ions derived from the plasma and collided with the wafer W.
FIG. 2 shows an example of a conventional spiral coil antenna, and FIGS. 3A and 3B show electric field distribution and density of plasma generated within the reaction chamber shown in FIG. 1 by the spiral coil antenna shown in FIG. 2, respectively. As shown in FIG. 2, the spiral coil antenna 30 is typically comprised of a single spirally wound conductive coil. However, the spiral coil antenna 30 has a disadvantage in that the magnitude of the electric field induced thereby is not uniform. That is, as shown in FIG. 3a, the electric field is relatively weak at the edge portion of the spiral coil antenna, and is strong at the center portion thereof. Therefore, the density of the plasma generated is highest at the center portion of the reaction chamber.
The most densely generated plasma at the center portion of the reaction chamber is diffused toward a wafer placed near the bottom of the reaction chamber. Consequently, the density of the plasma in an area near the wafer surface where reaction between the plasma and the wafer occurs is high at the center portion of the area near the wafer surface, and is low at the edge portions of the area near the wafer surface. Such irregular distribution of the plasma density causes a problem of the depth to which the wafer or substrate is etched or the thickness to which a material is deposited on the wafer or substrate being non-uniform over the surface thereof. As the diameter of the reaction chamber is increased to accommodate larger wafers, this non-uniformity problem becomes more serious. Further, in order to keep the plasma density sufficiently high within the reaction chamber, the radius of the antenna 30 and the number of turns of the coil should be increased to conform to the increased size of the ICP equipment. However, increasing the number of turns of the coil causes another problem in that the self-inductance of the antenna increases, and accordingly, the efficiency of the plasma discharges is degraded.
FIGS. 4A through 4C show various antennas that have been proposed to solve the above-described problems of coil antennas. FIG. 4A shows an antenna 40 disclosed in U.S. Pat. No. 5,401,350, which includes a spiral coil antenna 40a placed on the upper portion of a reaction chamber 42, and an additional solenoid-type antenna 40b wound around the outer surfaces of the sidewalls of the reaction chamber 42. The antenna 40 shown in FIG. 4A compensates for the low plasma density at the edge portions of the reaction chamber 42 to solve the problem of the non-uniform plasma density distribution that is encountered with the conventional spiral coil antenna described above. However, since the additional antenna 40b is wound around the outer surfaces of the sidewalls of the reaction chamber 42, the portions of the reaction chamber 42 corresponding to the antenna 40b should be made of a dielectric substance. Further, an additional coolant passage should be provided for cooling the antenna 40b. Therefore, the antenna as shown in FIG. 4A has a problem in that the entire size of the apparatus increases.
FIG. 4B shows another antenna 50 disclosed in U.S. Pat. No. 6,291,793, which includes a plurality of spiral coils 52, 54, and 56 branching off in parallel. The multiple and parallel type antenna 50 shown in FIG. 4B has a merit in that the self-inductance of the antenna 50 can be lowered as the number of branching off coils 52, 54, and 56 increases. However, such multiple and parallel type antenna has disadvantages in that the density of the plasma generated at the center portion of the antenna 50 is low, and parameters for controlling the uniformity of the plasma density distribution are limited.
FIG. 4C shows another antenna 60 disclosed in U.S. Pat. No. 6,080,271, wherein current flows in adjacent coils 62 and 64 in opposite directions. In the case of the conventional spiral coil antenna wherein current flows in each coil in the same direction, the magnetic fields produced around the adjacent coils are counterbalanced. However, in the case of the antenna 60 shown in FIG. 4C, the magnetic fields generated around the adjacent coils 62 and 64 reinforce each other. Accordingly, the antenna 60 of FIG. 4C has an advantage in that the inductance of the antenna is lowered. However, since the intensity of the inductive electric field is decreased, and therefore, the plasma density is lowered, there is a problem in that a magnetic core should be used to compensate for the reduced intensity of the electric field.
Due to the problems described above, the conventional antennas disclosed so far have shortcomings in adequately conforming to variations in process conditions to obtain high plasma uniformity. Particularly, as wafers become larger, it is more difficult to maintain uniform plasma density near the edge portions of the wafers using the conventional antennas, and as a result, the quality and yield of semiconductor devices are seriously deteriorated.
The present invention provides an inductively coupled plasma generating apparatus incorporating a double-layered antenna system with lower and upper coil antennas to improve uniformity of plasma density around a substrate within a reaction chamber.
An inductively coupled plasma generating apparatus according to the present invention includes a reaction chamber having an inner space kept in a vacuum state; an antenna system installed at an upper portion of the reaction chamber to induce an electric field for ionizing reaction gas supplied into the reaction chamber and generating plasma; and an RF power source connected to the antenna system to supply RF power to the antenna system, wherein the antenna system includes a lower antenna installed in adjacent to the upper portion of the reaction chamber, and an upper antenna installed a predetermined distance above the lower antenna.
According to an embodiment of the present invention, it is preferable that the upper antenna is installed to correspond to edge portions of a substrate placed within the reaction chamber.
In such embodiment of the present invention, it is preferable that the upper antenna includes a single-wire circular coil having either one or two turns.
Further, it is preferable that the lower antenna includes either a spiral coil having a predetermined number of turns or a plurality of concentric, connected circular coils.
Furthermore, the lower and the upper antennas preferably are connected in parallel with a single power source. However, the lower and the upper antennas may have different RF power sources.
According to another embodiment of the present invention, it is preferable that the lower and the upper antennas respectively include an outside antenna placed to correspond to edge portions of a substrate within the reaction chamber, and an inside antenna placed inside the outside antenna with a predetermined space therebetween.
In such embodiment of the present invention, it is preferable that current flows opposite directions through the adjacent inside and outside antennas and in the same direction through the adjacent upper and lower antennas adjacent.
Further, two single-wire coils are placed to cross each other and extend up and down, and outside and inside so as to configure upper outside, lower outside, upper inside, and lower inside antennas.
Furthermore, the two single-wire coils are connected in parallel with a single power source. However, the two single-wire coils may have different RF power sources.
According to the present invention, the uniformity of the plasma density distribution around the substrate within the reaction chamber can be controlled by adjusting the positions of an upper or an inside antenna.